Natural gas prices, based on the twelve-month average of the first of the month Henry Hub index price, were $3.598 per MMBtu in 2021 as compared to $1.985 per MMBtu in 2020, and $2.581 per MMBtu in 2019. Through November 1, 2022, the twelve-month average of the first of the month Henry Hub index price is $6.166 per MMBtu. Oil prices, based on the NYMEX first of the month average price, were $66.56 per barrel in 2021 as compared to $39.57 per barrel in 2020, and $55.69 per barrel in 2019. Through November 1, 2022, the NYMEX first of the month average price was $92.37. Since January 1, 2021, we have not filed any estimates of our oil and gas reserves with, nor were any such estimates included in any reports to, any federal authority or agency, other than the Securities and Exchange Commission.
Maintaining a strong balance sheet and ample liquidity are key components of our business strategy. In 2022, we will continue our focus on preserving financial flexibility and ample liquidity as we manage the risks facing our industry. Our capital budget for the year is reflective of current commodity prices and has been established based on an expectation of available cash flows, with any cash flow deficiencies expected to be funded by borrowings under our revolving credit facility. As we have done historically to preserve or enhance liquidity, we may adjust our capital program throughout the year, divest non-strategic assets, or enter into strategic joint ventures.
In the third quarter of 2021, nine two-mile horizontal wells in Upton County, Texas, operated by Apache Corporation, were completed and brought into production. In the fourth quarter of 2021, three two-mile horizontal wells operated by Ovintiv Mid-Continent in Canadian County, Oklahoma were completed and brought online in January 2022. The Company has an average of 47.5% interest in the nine wells completed with Apache and 11.25% interest in the three wells completed with Ovintiv.
In the second quarter of 2022, the Company participated with SEM Operating Company LLC in the drilling of four 7,900’ horizontal wells in Irion County, Texas with 10.3% interest. These four wells began their production in August. Also in the second quarter of 2022, the Company participated in the drilling of four 10,000’-long horizontal wells in Canadian County, Oklahoma with 9.38% interest. These four wells, operated by Ovintiv Mid-Continent, were also put into production in early August of this year. In the fourth quarter of this year another fifteen wells are planned to be spud.
Since the start of our West Texas horizontal drilling program in 2015, we have participated in 81 wells and invested approximately $130 million in horizontal drilling in the Permian Basin. This includes the four wells currently in progress with SEM Operating Company in Irion County, Texas.
In Upton County, Texas, we are developing a contiguous 3,260-acre block with our joint venture partner, Apache Corporation. In this block the Company has 2,600 leasehold acres with interest between 14% and 56% depending on the particular lease and depth being developed. In 2018, eight successful wells were drilled horizontally by Apache Corporation in the Wolfcamp “B” of this block with the Company participating for 49% interest and this is believed to be full development of the Wolfcamp “B” reservoir. Together with Apache, we are planning development of the Upper Wolfcamp, Jo Mill, and Lower Spraberry reservoirs of this block. These shallower reservoirs have been proven-up on our offset 1,300-acre Kashmir tract. It is expected that as many as 36 additional horizontals will be developed on this 3,260-acres in the near future. This development is estimated to cost approximately $387.0 million, with the Company’s share being approximately $174.4 million. Two 3-mile-long horizontals have been slated for the first quarter of 2023. In addition to the 36 prospective wells to be drilled for these three reservoirs, a fourth target reservoir, the Middle Spraberry, is also prospective for future development. The potential of the Middle Spraberry on the 3,260-acre block is for 12 horizontal wells to be drilled and completed at a gross cost of approximately $138.0 million with the Company’s share being approximately $63.0 million. The actual number of wells that are eventually drilled as well as the cost and the timing of drilling will vary based upon many factors, including commodity market conditions.
In addition to the 3,260-acre block being developed, as described above, the Company has also been developing an offsetting 1,300-acre block in Upton County, Texas, with Apache Corporation as operator. In the second quarter of 2019 three horizontal wells were completed and brought on production from reservoirs above the Middle Wolfcamp: one in the Wolfcamp “A”, one in the Jo Mill, and one in the Lower Spraberry, confirming the economic viability of these reservoirs on our acreage. Prime holds 47.5% working interest in these reservoirs. As a result of the success of the initial three wells, nine additional horizontals followed and were completed in the third quarter of 2021. Our average 47.5% share of the cost of these nine horizontal wells was approximately $26.7 million in total. In addition to the Wolfcamp “A”, Jo Mill and Lower Spraberry, that are now considered fully developed on the tract, four locations in the Middle Spraberry will be considered for future development at an estimated gross cost of approximately $40.0 million with the Company’s share being approximately $18.8 million.
Also in the Permian Basin of West Texas, we are developing a 965-acre block with ConocoPhillips in Martin County, Texas. In 2016 and 2017, four horizontal wells were drilled, completed, and put on production. The Company owns 35% to 38% interest in this joint venture acreage where we have the potential to drill as many as 36 additional wells.
18